The present invention relates to a new and useful composition comprising a mixture of two or more herbicides and a method for preparing such a composition. More particularly, the present invention relates to a stable agriculturally acceptable herbicidal mixture of a 2-chloroacetamide herbicide dissolved in an organic solvent and an imidazolinone herbicide in acid form stably suspended as a separate phase in finely divided form and to a method for formulating such a mixture.
2-Chloroacetamide herbicides and especially 2-chloroacetanilide herbicides are known to be particularly useful when applied preemergent or early postemergent to control annual grasses and many broad-leaved weeds in a variety of crops, including cotton, corn, oilseed rape, peanuts, soybeans, sugarcane, etc.
Imidazolinone herbicides such as imazaquin are known to be especially effective when applied by means of preplant incorporation, preemergent and early postemergent techniques against broad-leaved and grass weeds and sedges to control weeds in soybeans, cowpeas, tobacco, etc. Unfortunately, formulated imazaquin loses an appreciable amount of its activity over passage of time. When 2-chloroacetamide herbicides and imidazolinone herbicides are used as mixtures, they complement each other's activity. Mixtures thereof provide desired control of a broader spectrum of weeds than that which can be controlled by the use of the 2-chloroacetamide herbicides alone or the imidazolinone herbicide alone. Unfortunately, formulations of the two herbicides prepared by conventional procedures are unstable, especially when the preferred acid form as distinguished from the water-soluble salt form of the imidazolinone herbicides is used. Difficulties in spraying such mixtures are commonly encountered. Heretofore, it has been found to be more convenient and effective to apply the two types of herbicides sequentially rather than to employ an unstable mixture of the two types of herbicides, even though spraying the two types of herbicides in a single application as a mixture affords obvious economic advantages over spraying the two types of herbicides as separate applications.
It is desirable, therefore, to prepare stable package mixes of a chloroacetamide herbicide and an imidazolinone herbicide which have extended shelf life and which can be conveniently sprayed on the plants to be controlled and wherein any reduction of activity due to chemical interaction between the two herbicides is substantially reduced.
Alachlor, which chemically is 2-chloro-2',6'-diethyl-N-methoxymethylacetanilide, and imazaquin, which chemically is (RS)-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) are two well-known herbicides used as preemergents which have individually enjoyed significant commercial success.
Alachlor technical is sold as Lasso.RTM. herbicide by Monsanto Company, St. Louis, Mo. and is used mainly as a pre-emergent herbicide.
Imazaquin is sold as Scepter.RTM. herbicide by American Cyanamid Co. (imazaquin-ammonium as 180 g/l acid equivalent).
While each of these herbicides has enjoyed commercial success individually, it is desired however to prepare a stable agriculturally acceptable concentrate composition comprising a herbicidally effective amount of each of alachlor and imazaquin which can be marketed as a concentrate and diluted with additional water and then applied in a single application to kill and control weeds or other vegetation in agriculture.
Package mixing of alachlor and imazaquin has not been successful heretofore because of the inherent instability of imazaquin in a neutralized salt form in the presence of alachlor, as well as because of the inability to stably suspend imazaquin in the acid form to provide a suitable emulsion. Forming mixtures of alachlor and imazaquin in which the imazaquin has been added as the ammonium salt may result in a composition, wherein the overall herbicidal activity of the two herbicides is substantially reduced. Attempts to develop mixtures of alachlor and imazaquin in which imazaquin was added as the solid acid form resulted in unacceptable formulations containing agglomerated imazaquin acid particles which during dilution with water, may result in clogging of sprayer nozzles and thus in reduction of effective weed control.
The process of this invention overcomes the above-discussed drawbacks of preparing a mixture of a 2-chloroacetamide herbicide and an imidazolinone herbicide by in-situ forming imazaquin acid particles during formulation of the mixture. The resulting imidazolinone acid particles are diminutive enough to remain stably suspended during storage of the mixture in concentrated form and later when used after dilution with water. These diminutive suspended particles do not clog sprayer nozzles; and the resulting spray provides herbicidal activity equivalent to sequential applications of a 2-chloroacetamide herbicide and an imidazolinone herbicide to weeds.